A confocal microscopic technique to determine the refractive index of soft tissues and its application to articular cartilage

Kuyu Wang

    Research output: ThesisDoctoral Thesis

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    Abstract

    [Truncated abstract] Articular cartilage (AC) is a thin and hyaline layer of tissue covering articulating ends to provide extremely low friction between the two opposing articular surface and maintain the contact stress arisen by external loads within a physiological safe range. Mechanical traumas induced by exercise injury or excessive wear can prevent the normal functions of AC and may further develop into pathological degeneration, such as osteoarthritis (OA). Currently, there is no universal technique that can accurately monitor the pathological progress of AC. Arthroscopy provides a new way to observe the morphological damage of AC in vivo, but is limited by its resolution and capability to detect early OA. The non-invasive detection of AC degeneration in a quantitative way is still a challenge. The current thesis thoroughly investigated the propagation of light (characterized as refractive index, RI) in AC tissue and the potential reaction of RI to AC samples with various degenerating conditions. A novel technique that can detect AC degeneration without damaging the tissue should be sensitive to the organizational and biochemical alterations in AC matrix. In addition, it should have the potential to be developed as an in vivo method. The study presented in this thesis proposed a reliable method based on confocal microscopy to measure RI of AC within a tiny spot (Chapter 3 and Chapter 6). The verification experiment demonstrated that the relative error of the proposed method was no more than 0.02%. With this technique, the RI distribution from articular surface to the deeper region could be accurately determined. Since RI characterizes the interaction between light and tissue constitutions around the light propagating path, RI distribution of AC has the potential to assess the compositional alteration in AC matrix, which further indicates pathological progress of cartilage. The current thesis characterized the distributions of RI in both normal and naturally degenerated AC (Chapter 4) with a step size of 50 μm from cartilage surface. The overall RI of immature AC (1.3975, fetal lamb) is lower than the mature AC (1.4444, sheep) harvested from the same position of femoral condyles. In normal AC, RI generally distributes as a regular ramp shape with little local fluctuation and peaks in middle-deep region. The degenerated AC, however, was detected with remarkable and irregular fluctuation. Quantitative assessments show that loss of proteoglycans can increase the level of RI fluctuation as well as overall RI of AC (Chapter 4). Despite an intimate correlation between the distribution of RI and the degenerating status of AC, experiments using AC samples with natural degeneration are still difficult to clarify the exact reaction of RI distribution induced by structural collapse and biochemical alteration. Thus, the mechanical wear and biochemical alteration were artificially imposed on AC samples collected from femoral condyles of kangaroos to explore their different effects on RI distribution (Chapter 5). The results suggest that mechanical wear had less impact to the depth distribution of RI unless the interstitial fluid was severely lost from AC matrix after long-term of external loading. However, enzymic digestion of AC samples induces severe RI fluctuation...
    Original languageEnglish
    QualificationDoctor of Philosophy
    Publication statusUnpublished - 2013

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